1. Field of the Invention
The present invention relates to lens modules and more particularly, to a lens module for use in a bill acceptor for detecting the authenticity of a bill, and the lens module has multiple positioning structures to have a lens device positively and accurately positioned in between a holder base and a top cover.
2. Description of the Related Art
Following fast development of technology, our mode of living has been changed. Various automatic vending machines (card dispensers, ticket vending machines, money exchanging machines, etc.) are used everywhere to sell any of a variety of products without serviceman. Providing automatic vending machines saves much labor cost, and brings great convenience to consumers. A money-exchanging machine generally comprises a coin acceptor and a bill acceptor.
However, venders and consumers are always assailed by the problem of counterfeit money since the use of paper currency. Following development of computer technology, evil persons may use a computer to scan, copy and print paper money. Therefore, a paper currency has anti-counterfeiting techniques. Visible anti-counterfeiting techniques of paper currency include paper material, ink, seal, mark and etc. that can easily be verified with the eyes. However, examining invisible anti-counterfeiting techniques requires a special machine or instrument to verity the authenticity. A validator for this purpose uses rollers to carry the inserted paper currency over a magnetic head, which detects the magnetic inks of the emblems and portrait and compares the detected signal with respective predetermined reference values for determining the authenticity of the paper current subject to the comparison result. However, the magnetic head tends to be contaminated by ink dirt, resulting in an inaccurate detection. Further, a counterfeit currency maker may make a counterfeit currency that carrying similar magnetic inks to cheat the machine.
Nowadays, modern valuable paper validators commonly use different LEDs (light emitting diodes) to emit different light for examining the characteristics of different paper currency. FIGS. 9 and 10 show a prior art valuable paper (bill) validator. This design of valuable paper validator comprises a first linear light source A1 and a second linear light source A2 disposed at two sides above a test zone F1, a plurality of photo sensors C1 set between the two linear light sources A1 and A2, and a first optical element B1 set below the photo sensors C1. When a document (valuable paper) E1 enters an inlet of the valuable paper validator, the inlet is blocked, and a sheet-transferring roller set is started to carry the document E1 through the test zone F1. At the same time the linear light sources A1 and A2 are controlled to emit pulsed light onto the document E1, the first optical element B1 condenses reflected light onto the photo sensors C1, and the photo sensors C1 feedback the detected value at a predetermined circulation time point. This detected value is indicative of the average PPF (paired-pulse facilitation) of the scanned surface color of the document E1. The aforesaid method is to examine the whole document. Further, a supplementary light source A4 and a fourth optical element B4 may be provided at the other side. The supplementary light source A4 is controlled to emit penetrative light that passes through the document E1 for checking the transmission of the document E1. After scanning, the operating unit of the valuable paper validator receives different values produced by different light sources and compares the values to storage reference values, thereby determining to accept or reject the document. According to this induction method, it is necessary to verify multiple strip blocks of the document E1 and to compare the scanned values produced by the strip blocks to reference values for further determination. According to this design, each linear light source A1 or A2 uses different colors of light emitting diodes A3 to emit different colors of light for verification. Further, a second optical element B2 and a third optical element B3 are set in front of the first linear light source A1 and the second linear light source A2 to correct the respective light source output angle. The arrangement of the linear light sources A1 and A2, the optical elements B1, B2 and B3 and the photo sensors C1 must be carefully calculated so that detected signals can be compared to reference values for further accurate determination.
The aforesaid prior art valuable paper validator has numerous drawbacks as outlined hereinafter.    1. Because the LEDs A3 in each linear light source A1 or A2 are spaced from one another at a distance, these LEDs A3 do not allow the document E1 to be examined at one same test zone F1 with different colors of light, and can only use the average value of all scanned light to calculate the surface color reaction of the document E1.    2. Different documents (paper currency) E1 from different countries have different anti-counterfeiting characteristics. Therefore, the main unit must provide a high capacity database for storing predetermined reference data for comparison.    3. This validation method uses the light emitting diodes A3 to emit different colors of light onto the document E1, and the photo sensors C1 with the first optical element B1 to collect reflected light from different strip blocks of the document E1 for comparing to reference values. The precision of the adjustment between the light emitting diodes A3, the photo sensors C1 and the optical elements B1, B2, and B3 is critical.    4. After scanning of different strip blocks of the document E1 with different colors of light from the light emitting diodes A3, a precision array computing procedure is necessary to verify the authenticity of the document E1. This computing procedure requires a certain length of time, not suitable for use in a vending machine to verify the authenticity of a paper money.    5. The complicated structure of this design of valuable paper validator uses so many parts, resulting in a high manufacturing cost.
Further, ATMs (Auto Teller Machines) or bill counters used in a banking system commonly use ultraviolet lamps to scan paper currency. Ultraviolet lamps are not suitable for use in a bill validator for vending machine. When an ultraviolet lamp type bill validator is used in an outdoor vending machine, air moisture may pass through gap between the lamp bulb and the electric socket, causing a short circuit. Further, the bulb of an ultraviolet lamp attenuates quickly with use. Further, an ultraviolet lamp consumes much electric power and releases much heat energy during operation. Further, an ultraviolet lamp has a big side and a short working life, and is easy to break.